The present invention relates to a computer system that continually changes off between a given realtime program and some other program. More particularly, the invention is directed to a computer system in which a clock-controlled switching signal carries on a cyclic alternation of at least one given realtime program providing realtime control operations for a peripheral device with at least one other program within each respective period of the clock signal.
Cyclical data processing is expedient for providing control and regulation functions in realtime applications. The input and output equipment of the realtime application, sensors and drivers, for example, form a control circuit. Typically, such a control circuit operates using a given constant time base, and this time base must be constant for all components of the control circuit.
Industrial control applications always connect a large number of peripheral devices. Often these devices are wide-spread and connected across a great distance to a controlling computer system. The data processing is then carried out using a communications system, for example over a process field bus connection. The communications system must guarantee that data is transferred in accordance with that given constant time base.
The performance of control and regulation functions within one or more realtime control programs takes place within the computer system while acyclic tasks within one or more non-realtime programs are performed: the viewing of processing data, for example.
The communications system should provide the time base for the overall process, that is, the overall process including the changes between realtime and non-realtime operations, which is the critical process management function.
European patent publication EP 1 067 448 A2 describes a computer system of the sort previously used for realtime and non-realtime programming. In this computer system a personal computer (PC) system is connected through a communications system to peripheral devices using one of the PC system's independent communications clocks, and a stronger time base clock can be generated from the communications clock.